My Fiat Bravo (99) Wont Start?

I have a fiat bravo 99 and it wont start i have brought it to two local mechanics and they dont know whats wrong with it the starter seems fine and the battery is not dead but it not igniting and when i do get it going (in some cases) i can hear a noise from the engine like you have a half full bottle of water and start tilting it from side to side can anyone help